The invention relates generally to electronic component packages and particularly to those which utilize an encapsulant. Even more particularly the invention relates to substrate packages for preventing cracks within the encapsulant from severing a conductive path therein.
Electronic component packages known in the art may include an encapsulant material. The encapsulant protects the mechanical and electronic bond between the package and the component by shielding the bond, typically solder, from the effects of dust, moisture, or contaminants in the environment which otherwise may weaken the bond or cause it to fail. The encapsulant may also provide mechanical strength to the bond, thereby reducing the effects of thermal stresses, mechanical flexing, vibration or other mechanical effects.
One such encapsulant structure and method of dispensing the encapsulant material is described in U.S. Pat. Nos. 6,228,680 6,245,583 and 6,213,347, which are hereby incorporated by reference. The encapsulant is applied to a semiconductor chip bonded in a flip-chip or xe2x80x9cC-4xe2x80x9d manner via solder bumps to a substrate package. The encapsulant is applied after the solder bumps are reflowed to fill the gap between the semiconductor chip and the substrate in order to strengthen the solder joints without affecting the electrical connections.
A polymeric precursor is dispensed onto the substrate adjacent the chip. The precursor is then heated, polymerized, and cured to form the encapsulant, using temperature profiles described in the above U.S. patents.
Passive components such as capacitors, resistors, diodes, switches, and the like may also be attached to mounting pads on a substrate. Proper alignment of such a component to the pad is described in U.S. Pat. Nos. 6,054,653 and 5,663,529.
For example, Hansen et al. In U.S. Pat. No. 6,054,653 describes a pad shape with at least two triangular portions to prevent the tendency of a surface mount component to move about or float and become misaligned when solder is melted to attach the surface mount component to a pad. The triangular portions are sized to provide a solder fillet formation to reliably attach the component to the pad.
McMillan II et al. in U.S. Pat. No. 5,663,529 describe a substrate pad having notches for defining registration edges. The registration edges along with surface tension forces produced by melting solder provide proper alignment of a heatsink component to the pad during reflow soldering. The mounting pad may be enlarged, except for the notches, to increase thermal transfer from the heatsink into a printed circuit board beneath the mounting pad.
Adams, Jr. et al. in U.S. Pat. No. 5,303,122 describe a mounting pad shape upon which different sized surface mount components can be mounted. Fing in U.S. Pat. No. 5,731,960 describe a low inductance decoupling capacitor arrangement in which a pad has a mounting region and a boundary region. The boundary region has low inductance via connections. A solder mask material is applied over the boundary region to prevent solder from being sucked into the vias and permitting the capacitor component to be aligned in the mounting region which is not solder masked.
When an encapsulant material is used with a surface mounted component for any purpose including those above, there may be a coefficient of thermal expansion (CTE) difference between the encapsulant and the component. This difference is especially severe with organic encapsulant materials applied to ceramic components mounted on organic substrates. The low CTE of surface mounted, ceramic capacitors, for example, creates high stress in an encapsulant filled, particularly at the corners of the ceramic component and cracking of the encapsulant there is common. Such a crack can then propagate into the dielectric substrate below, just beyond the component periphery causing cracks in underlying circuit lines within the substrate. These cracks may sever the electrical continuity of the line or produce an unreliable connection subject to failure under normal thermal or mechanical stresses.
Organic substrates with thin organic layers having thin narrow circuit lines are particularly susceptible to failure from crack propagation because the thin layers and lines have little strength to resist a crack originating in the encapsulant, which otherwise might not cause a failure.
None of the aforementioned documents provide a recognition of this cracking problem or offer a solution thereto. It is believed that a solution to this now identified problem would constitute a significant advancement in the component packaging art.
It is therefore a principal object of the present invention to enhance the electronic component packaging art by providing a package with enhanced resistance to crack porpagation.
It is another object to provide such a package wherein enhanced resistance to crack propagation is possible.
It is a further object to provide such a package which can be produced in a relatively inexpensive manner and is particularly adapted for mass production.
These and other objects are attained in accordance with one embodiment of the invention wherein there is provided an electronic package, comprising a substrate of dielectric material having at least one conductive path therein, a conductive pad on an outer surface of the substrate, having an electronic component coupled thereto, a quantity of encapsulant material substantially surrounding the electronic component along the sides thereof, and wherein the conductive pad extends from substantially beneath the electronic component to beyond the outer periphery of the encapsulant material to substantially prevent cracks within the encapsulant material from spreading into the dielectric material and severing the conductive path.
In accordance with another embodiment of the invention there is provided a component packaging structure, comprising, a dielectric substrate having a conductive path therein, a metallic component mounting pad on an outer surface of the dielectric substrate, having an electronic component attached thereto, encapsulant material positioned along a side of the electronic component, and wherein said mounting pad extends outward from the side of the electronic component substantially beyond the encapsulant material to substantially prevent a crack within the encapsulant material from propagating into the dielectric substrate and opening the conductive path.